| Paper | Title | Page |
|---|---|---|
| THPMS001 | An Ideal Circular Charged-Particle Beam System | 2999 |
|
||
|
Funding: Research at Massachusetts Institute of Technology was supported by DOE, Office of High-Energy Physics, Grant No. DE-FG02-95ER40919 and AFOSR, Grant No. FA9550-06-1-0269. A theory is presented for the design of an ideal non-relativistic circular beam system including a charged-particle emitting diode, a diode aperture, a circular beam tunnel, and a focusing magnetic field that matches the beam from the emitter to the beam tunnel. The magnetic field is determined by balancing the forces throughout the gun and transport sections of the beam system. OMNITRAK simulations are performed, validating theory. As applications, a circular electron beam system is discussed for space-charge-dominated beam experiments such as the University of Maryland Electron Ring (UMER), and a circular ion beam system is discussed for high energy density physics (HEDP) research. |
||
| THPMS005 | Observation of Wakefields in a 17 GHz Metallic Photonic Bandgap (PBG) Structure | 3002 |
|
||
|
Funding: Work supported by the Department of Energy, High Energy Physics, under contract DE-FG02-91ER40648. Results are reported on experimental wakefield measurements made on a 6 cell, 17 GHz metallic PBG accelerator structure. Wakefields were observed using a variety of detectors and methods. The PBG structure is open, containing no outer wall, and radiation has been observed through a window in the surrounding vacuum vessel. The input and output ports have also been used with windows to observe radiation coupling out of the ports. Estimations of radiation are made using HFSS and an EFIE code. Measurements have been made using video diode detectors, wavemeters, heterodyne receivers, and a bolometer. Plans are discussed for future experiments with injected power and longer structures. |
||
| THPMS006 | Photonic Bandgap (PBG) Accelerator Structure Design | 3005 |
|
||
|
Funding: Work supported by the Department of Energy, High Energy Physics, under contract DE-FG02-91ER40648. High gradient structure design entails optimization of the gradient, while minimizing surface electric fields (associated with breakdown) and surface magnetic fields (associated with pulsed heating). Design studies are reported comparing metallic and dielectric PBG structures and standard disk-loaded waveguide. Operation in a higher order mode is considered. A variety of codes; HFSS, CST MWS, and Superfish have been used to compare and refine designs. Final design work is in preparation for a structure to be cold tested, tuned, and then processed to high gradient operation at the MIT HRC 17 GHz accelerator facility. |
||
| THPMS007 | Surface Waves on Interface of 3D Metal-wire Diamond Lattice for Accelerator Applications. | 3008 |
|
||
|
Funding: Dept. of Energy, High Energy Physics We present the results of our recent research on 3D metal-wire lattices operating at microwave frequencies, with applications to advanced accelerator structures and radiation sources based on the Smith-Purcell effect. Bulk and surface electromagnetic waves supported by a diamond-like lattice are calculated using HFSS. The bulk modes are determined using primitive cell calculations. The surface mode is determined using the simulations of the stack of cells with the perfect-matching layer (PML) boundary. |
||
| THPMS010 | Polarized Pulsed Beam Source for Electron Microscopy | 3011 |
|
||
| A novel source of polarized pulsed electron beam is discussed. Unlike conventional devices based either on a thermionic cathodes or field-emission needle cathodes, in this source the electrons are produced by a laser beam hitting the cathode surface. Using a combination of gallium arsenide (GaAs) planar cathode and a suitable laser one can obtain a polarized picosecond electron bunch. Numerical simulations of the electron dynamics in the optimized cathode-anode geometry have shown that the beam with initial transverse size of a few mm can be focused down to 1 mm RMS at a distance of about 4 cm from the cathode. The suggested source can be installed instead of a tungsten filament source in an existing electron microscope with no modification of any column elements. The main advantages of this approach are that the beam can be easily pulsed, the beam is polarized which makes it an effective probe of some magnetic phenomena, and the laser can be used to provide larger beam intensity. The design of the source and subsequent fabrication has been completed. The paper presents numerical studies, conceptual design of the device, and results of beam measurements. | ||
| THPMS011 | Design Considerations and Modeling Results for ILC Damping Ring Wigglers Based on the CESR-c Superconducting Wiggler | 3014 |
|
||
|
Funding: Funding provided by NSF grant PHY-0202078 The ILC damping rings require wiggler magnets with large physical aperture and with excellent field quality to maintain the dynamic aperture of the rings. We consider two possible designs derived from the wigglers presently in operation at the Cornell Electron Storage Ring. Design optimization has been performed based on detailed tracking calculations of dynamic aperture and tune footprint in a full model of the damping ring. Results of finite-element modeling, transfer functions, and the accuracy of analytic models of the wiggler field will be discussed. |
||
| THPMS012 | Collection Optics for ILC Positron Target | 3017 |
|
Funding: NSF We are considering the implementation of a Lithium lens and SC solenoidal lens for collection of positrons in ILC undulator-based source. Such a lens installed right after the thin target, which is illuminated by gamma quants from helical undulator. |
||
| THPMS013 | Comparison of Tracking Codes for the International Linear Collider | 3020 |
|
||
|
Funding: Supported by the US Department of Energy, the US National Science Foundation and the Commission of the European Communities under the 6th Framework Programme "Structuring the European Research Area". In an effort to compare beam dynamics and create a ‘‘benchmark'' for Dispersion Free Steering (DFS) a comparison was made between different International Linear Collider (ILC) simulation programs while performing DFS. This study consisted of three parts. First, a simple betatron oscillation was tracked through each code. Secondly, a set of component misalignments and corrector settings generated from one program was read into the other to confirm similar emittance dilution. Thirdly, given the same set of component misalignments DFS was performed independently in each program and the resulting emittance dilution was compared. Performance was found to agree exceptionally well in all three studies. |
||
| THPMS014 | Design of a High Field Stress, Velvet Cathode for the Flash X-Ray (FXR) Induction Accelerator | 3023 |
|
||
|
Funding: This work was performed under the auspices of the U. S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48. A new cathode design has been proposed for the Flash X-Ray (FXR) induction linear accelerator with the goal of lowering the beam emittance. The present design uses a conventional Pierce geometry and applies a peak field of 134 kV/cm (no beam) to the velvet emission surface. Voltage/current measurements indicate that the velvet begins emitting near this peak field value and images of the cathode show a very non-uniform distribution of plasma light. The new design has a flat cathode/shroud profile that allows for a peak field stress of 230 kV/cm on the velvet. The emission area is reduced by about a factor of four to generate the same total current due to the greater field stress. The relatively fast acceleration of the beam, approximately 2.5 MeV in 10 cm, reduces space charge forces that tend to hollow the beam for a flat, non-Pierce geometry. The higher field stress achieved with the same rise time is expected to lead to an earlier and more uniform plasma formation over the velvet surface. Simulations of the proposed design are presented. |
||
| THPMS015 | Observation of Multi-GeV Breakdown Thresholds in Dielectric Wakefield Structures | 3026 |
|
||
|
Funding: This work was performed under the auspices of the US Department of Energy under Contracts No. DE-FG03-92ER40693, DE-AC02-76SF00515, W-7405-ENG-48, and DE-FG02-92-ER40745. The breakdown threshold of a dielectric subjected to the GV/m-scale electric-fields of an intense electron-beam has been measured. In this experiment at the Final Focus Test Beam (FFTB) facility, the 30 GeV SLAC electron beam was focused down and propagated through short fused-silica capillary-tubes with internal diameters of as little as 100 microns. The electric field at the inner surface of the tubes was varied from about 1 GV/m to 22 GV/m by adjusting the longitudinal compression of the electron bunch. The onset of breakdown, as indicated by a bright discharge, was found to correlate to a surface field of about 4 GV/m. An analysis of the damage sustained to the beam-exposed fibers, and its correlation to field amplitude, is also reported. |
||
| THPMS016 | A Large-Format Imaging Optics System for Fast Neutron Radiography | 3029 |
|
||
|
Funding: This work was performed under the auspices of the U. S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48. As part of the ongoing development of fast neutron imaging technology for national secu-rity applications at LLNL, a large-format imaging optics system has been designed and built. The system will be used to acquire radiographic images of heavily-shielded low-Z objects irradiated by ~ 10 MeV neutrons and is expected to have an ultimate spatial resolution ~ 1 mm (FWHM). It is comprised of a 65 cm x 65 cm plastic scintillator (e.g. BC-408), an aluminized front-surface turning mirror and a fast (~ f/1.25) optical lens coupled to a CCD camera body with a cryo-cooled, back-illuminated 4096 x 4096 (15 micron) pixel sensor. The lens and camera were developed and purchased from vendors and system integration was done at LLNL. A description of the overall system and its initial performance characteristics shall be presented. |
||
| THPMS017 | Design of Muon Accelerators for an Advanced Muon Facility | 3032 |
|
||
| Muon beams are produced at Muon Facilities all over the world. They are commonly used in condensed matter physics with mSR (Muon Spin Rotation / Relaxation / Resonance) spectroscopy. Up to today, the applications of mSR are limited by the large sizes of the muon beams (typically 10 cm2). We carried out design works of an Advanced Muon Facility at LANSCE that produces a 'muonμbeam'. The muonμbeam improves beam brightness by three orders of magnitude from that at conventional Muon Facilities and would revolutionize not only material research using mSR spectroscopy but also numerous applications in nano-technology, high-pressure science and bioscience. The designed facility mainly consists of a large acceptance muon channel 'LA Omega' followed by novel muon linear accelerators. This equipment is capable of producing the world?s most intense muon beam of ~109 muon/s at LANSCE. The intense muon beam of LA Omega will be cooled and accelerated with the muon linear accelerators to produce a 50-keV and a separate 10-MeV muonμbeam. The unique time structure of the muon beam produced by the LANSCE linear accelerator optimally matches the muon accelerator. | ||
| THPMS018 | High Average Current Betatrons for Industrial and Security Applications | 3035 |
|
||
|
Funding: DOE Grant DE-FG02-04ER84051 The fixed-field alternating-gradient (FFAG) betatron has emerged as a viable alternative to RF linacs as a source of high-energy radiation for industrial and security applications. For industrial applications, high average currents at modest relativistic electron beam energies, typically in the 5 to 10 MeV range, are desired for medical product sterilization, food irradiation and materials processing. For security applications, high power x-rays in the 3 to 20 MeV range are needed for rapid screening of cargo containers and vehicles. In a FFAG betatron, high-power output is possible due to high duty factor and fast acceleration cycle: electrons are injected and accelerated in a quasi-CW mode while being confined and focused in the fixed-field alternating-gradient lattice. The beam is accelerated via magnetic induction from a betatron core made with modern low-loss magnetic materials. Here we present the design and status of a prototype FFAG betatron, called the Radiatron, as well as future prospects for these machines. |
||
| THPMS019 | Comparison of 6D Ring Cooler Schemes and Dipole Cooler for Mu+Mu- Collider Development | 3038 |
|
||
| We discuss the various schemes to use ring coolers for 6D cooling for Mu+Mu- colliders. The earliest successful cooler used dipoles and quadrupoles and a high dispersion low beta region. This was also proposed in the form of solenoids. Recently, there have been many new ideas. The simplest is to use a simple dipole ring with high-pressure gas absorber or Li hydride. We show the results of simulations and compare with the results for other cooler schemes. | ||
| THPMS020 | Beam-Driven Dielectric Wakefield Accelerating Structure as a THz Radiation Source | 3041 |
|
||
|
Funding: United States Department of Energy Experimental work is planned to study the performance of a beam-driven cylindrical dielectric wakefield accelerating structure as a source of THz coherent Cerenkov radiation. For an appropriate choice of dielectric tube geometry and driving electron bunch parameters, the device operates in a single-mode regime, producing narrow-band radiation in the THz range. This source can potentially produce high power levels relative to currently available sources, with ~50 μJ radiated energy per pulse achievable using the electron beam currently in operation at the Neptune Advanced Accelerator Research Laboratory at UCLA (~13 MeV beam energy, ~200 μm RMS bunch length, ~500 pC bunch charge). Preparations underway for installation of the experiment are discussed. |
||
| THPMS021 | Optimum Electron Bunch Creation in a Photoinjector Using Space Charge Expansion | 3044 |
|
||
| Recent studies have shown that by illuminating a photocathode with an ultra-short laser pulse of appropriate transverse profile, a uniform density, ellipsoidally shaped electron bunch can be dynamically formed. Linear space-charge fields then exist in all dimensions inside of the bunch, which minimizes emittance growth. Here we study this process, and its marriage to the standard emittance compensation scenario that is implemented in most modern photoinjectors. We show that the two processes are compatible, with simulations indicating that a very high brightness beam can be obtained. An initial time-resolved experiment has been performed at the SPARC injector in Frascati, involving Cerenkov radiation produced at an aerogel. We discuss the results of this preliminary experiment, as well as plans for future experiments to resolve the ellipsoidal bunch shape at low energy. Future measurements at high energy based on fs resolution RF sweepers are also discussed. | ||
| THPMS022 | 6 Dimensional Muon Phase Space Cooling by Using Curved Lithium Lenses | 3047 |
|
||
| A curved Lithium lens ring model can provide the emittance exchange mechanism in obtaining the muon 6 dimensional phase space cooling. With straight Lithium lenses in a muon cooling ring, only transverse phase space cooling has been demonstrated. We demonstrate the 6 dimensional phase space cooling with various parameters of a muon cooling ring in tracking simulation. | ||
| THPMS023 | Designing LWFA in the Blowout Regime | 3050 |
|
||
|
Funding: This work was supported by DOE and NSF under grant Nos. DE-FG03-92ER40727, DE-FC02-01ER41179, DE-FG02-03ER54721, and NSF-Phy-0321345. The extraordinary ability of space-charge waves in plasmas to accelerate charged particles at gradients that are orders of magnitude greater than that in current accelerators has been well documented. We develop a phenomenological framework for Laser Wakefield Acceleration (LWFA) in the 3D nonlinear regime, in which the plasma electrons are expelled by the radiation pressure of a short pulse laser, leading to nearly complete blowout. This theory provides a recipe for designing a LWFA for given laser and plasma parameters and estimates the number and the energy of the accelerated electrons whether self-injected or externally injected. These formulas apply for self-guided as well as externally guided pulses (e.g. by plasma channels). Based on this theory, we will present scenarios on how to build a single stage accelerator with output energies from GeV to TeV. Particle-In-Cell (PIC) simulations are used to verify our theory. This work was supported by DOE and NSF under grant Nos. DE-FG03-92ER40727, DE-FC02-01ER41179, DE-FG02-03ER54721, and NSF-Phy-0321345. |
||
| THPMS024 | Experimental Investigation of Self-guiding using a Matched Laser Beam in a cm Scale Length Underdense Plasma | 3052 |
|
||
|
Funding: This work was supported by NNSA Grant no. DE-FG52- 03NA00138, and DOE Grant no. DE-FG02-92ER40727.
High-intensity short-pulse laser guiding in plasma channels has extended the length over which acceleration occurs in laser wake field accelerators*. Recent multidimensional nonlinear plasma wave theory predicts a range of optimal characteristics for self-guiding of laser pulses in the blowout regime for pulses shorter than a plasma wavelength**. This theory predicts a robust, stable parameter space for self-guiding and wake production and has been verified through multidimensional particle-in-cell simulations. We experimentally explore the plasma dynamics and laser pulse propagation using a 50 fs multi-terawatt Ti:Sapphire laser in a helium plasma at plasma densities, laser powers, and spot sizes within this parameter space. Our parameters are in the range where the plasma is underdense and the laser power is much greater than the critical power for self focusing. The evolution of the laser pulse and plasma channel will be followed over several Rayleigh lengths.
* C. Geddes et. al., Nature (London) 431, 538 (2004)** W. Lu et. al., Phys. Plasmas 13, 056709 (2006) |
||
| THPMS026 | The UCLA Helical Permanent-Magnet Inverse Free Electron Laser | 3055 |
|
||
| The Inverse Free Electron Laser (IFEL) is capable, in principle, of reaching accelerating gradients of up to 1 GV/m making it a prospective accelerator scheme for linear colliders. The Neptune IFEL at UCLA utilizes a 15 MeV Photoinjector-generated electron beam of 0.5 nC and a CO2 laser with peak energy of up to 100 J, and will be able to accelerate electrons to 100 MeV over an 80 cm long, novel helical permanent-magnet undulator. Past IFELs have been limited in their average accelerating gradient due to the Gouy phase shift caused by tight focusing of the drive laser. Here, laser guiding is implemented via an innovative Open Iris-Loaded Waveguide Structure scheme which ensures that the laser mode size and wave front are conserved through the undulator. The results of the first phase of the experiment are discussed in this paper, including the design and construction of a short micro-bunching undulator, testing of the OILS waveguide, as well as the results of corresponding simulations. | ||
| THPMS027 | Dielectric Wakefield Accelerator Experiments at the SABER Facility | 3058 |
|
||
|
Funding: Work supported in part by Department of Energy contracts DE-AC02-76SF00515, DE-FG02-92-ER40745, DE-FG03-92ER40693 and W-7405-ENG-48 Electron bunches with the unparalleled combination of high charge, low emittances, and short time duration, as first produced at the SLAC FFTB, are foreseen to be produced soon at the SABER facility. These types of bunches have enabled wakefield driven accelerating schemes of >10 GV/m. In the context of the Dielectric Wakefield Accelerators (DWA) such beams, having rms bunch length as short as 20 um, have been used to drive 100 μm and 200 μm ID hollow tubes above 20 GV/m surface fields. These FFTB tests enabled the measurement of a breakdown threshold in excess of 4 GV/m (2 GV/m accelerating field) in fused silica. With the construction and commissioning of the SABER facility at SLAC, new experiments are made possible to test further aspects of DWAs including materials, tube geometrical variations, direct measurements of the Cerenkov fields, and proof of acceleration in tubes >10 cm in length. The E169 collaboration will investigate breakdown thresholds and accelerating fields in new materials including CVD diamond. Here we describe the experimental plans, beam parameters, simulations, and progress to date as well as future prospects for machines based of DWA structures. |
||
| THPMS028 | The Physical Picture of Beam Loading in the Blowout Regime | 3061 |
|
||
|
Funding: This work is supported by DOE and NSF under grant Nos. DE-FG03-92ER40727, DE-FC02-01ER41179, DE-FG02-03ER54721, and NSF-Phy-0321345. The realization of high quality LWFA-produced electron beams requires laser pulses that remain focused for distances exceeding the Rayleigh length. It is often thought that a short pulse laser cannot be self-guided and some form of external optical guiding is needed. As short pulse lasers with higher power are rapidly coming online to test the LWFA concept it is vital to understand the nature of their propagation through centimeters of plasma. We argue that a degree of self-guiding is possible for short ultra-intense pulses that have been shown to lead to complete ponderomotive expulsion of plasma electrons. Furthermore, the generation of a high quality electron beam requires proper loading of the wake. We have developed a theoretical framework which predicts the maximum number of electrons which can be loaded in the wake, as well as the optimal charge density profile for beam loading. Using the PIC codes OSIRIS and QuickPIC we present designs of LWFA accelerators that verify our theoretical estimates as well as demonstrate the potential of LWFA to produce high energy electron beams with high beam quality. |
||
| THPMS029 | Beam Head Erosion in Self-ionized Plasma Wakefield Accelerators | 3064 |
|
||
|
Funding: Work supported by Department of Energy contracts DE-AC02-76SF00515, DE-FG02-92ER40727, DE-FG02-92-ER40745 DE-FG02-03ER54721, DE-FC02-01ER41179 and NSF grant Phy-0321345
In the recent plasma wakefield accelerator experiments at SLAC, the energy of the particles in the tail of the 42 GeV electron beam were doubled in less than one meter [1]. Simulations suggest that the acceleration length was limited by a new phenomenon – beam head erosion in self-ionized plasmas. In vacuum, a particle beam expands transversely in a distance given by beta*. In the blowout regime of a plasma wakefield [2], the majority of the beam is focused by the ion channel, while the beam head slowly spreads since it takes a finite time for the ion channel to form. It is observed that in self-ionized plasmas, the head spreading is exacerbated compared to that in pre-ionized plasmas, causing the ionization front to move backward (erode). A simple theoretical model is used to estimate the upper limit of the erosion rate for a bi-gaussian beam by assuming free expansion of the beam head before the ionization front. Comparison with simulations suggests that half this maximum value can serve as an estimate for the erosion rate. Critical parameters to the erosion rate are discussed.
[1] I. Blumenfeld et al., Nature 445, 741(2007)[2] J. B. Rosenzweig et al., Phys. Rev. A 44, R6189 (1991) |
||
| THPMS030 | Mitigation of Ion Motion in Future Plasma Wakefield Accelerators | 3067 |
|
||
|
Funding: DoE contract # DE-FG02-92-ER40745 Simulation and analysis of the ion motion and multiple ionization in a plasma wakefield accelerator is presented for the parameters required of a future ILC afterburner. We show that although ion motion leads to substantial emittance growth for extreme parameters of future colliders in the sub-micron spot size regime, several factors that can mitigate the effect are explored. These include sunchrotron damping, plasma density gradient and hot plasma. |
||
| THPMS031 | Plasma Wakefield Acceleration Utilizing Multiple Electron Bunches | 3070 |
|
||
|
Funding: DoE contract # DE-FG02-92-ER40745 We investigate various plasma wakefield accelerator schemes that rely on multiple electron bunches to drive a large amplitude plasma wave, which are followed by a witness bunch at a phase where it will sample the high acceleration gradient and gain energy. Experimental verifications of various two bunch schemes are available in the literature; here we provide analytical calculations and numerical simulations of the wakefield dependency and the transformer ratio when M drive bunches and one witness bunch are fed into a high density plasma, where M is between 2 and 10. This is a favorable setup since the bunches can be adjusted such that the transformer ratio and the efficiency of the accelerator are enhanced compared to single bunch schemes. The possibility of a five bunch ILC afterburner to accelerate a witness bunch from 100 GeV to 500 GeV is also examined. |
||
| THPMS032 | Plasma Wakefield Acceleration Experiments using Two Subpicosecond Electron Bunches | 3073 |
|
||
|
Funding: This work is supported by US DoE under contracts DE-FG02-92-ER40745 and DE-FG02-04ER41294. Two ~100 fs electron bunches, separated in energy by approximately 1.8 MeV and in time by 0.5-1 ps, were sent through a capillary discharge plasma. The plasma density was varied from ~1·1014/cc to ~1·1017/cc. A 2-D PWFA model indicates the net wakefield produced by the bunches will depend on their relative charge, temporal separation, and the plasma density. This will affect the amount of energy gain or loss of the second bunch. During measurements of the energy spectrum of the second bunch, we observed a difference in the amount of gain or loss depending on the plasma density, which is consistent with the model prediction. |
||
| THPMS033 | Scaling of Energy Gain with Plasma Parameters in a Plasma Wakefield Accelerator | 3076 |
|
||
|
Funding: This work was supported by the Department of Energy contracts DE-AC02-76SF00515, DE-FG02-92ER40727, DE-FG02-92-ER40745. DE-FG02-03ER54721, DE-FC02-01ER41179 and NSF grant Phy-0321345.
Systematic measurements of energy gain as a function of plasma parameters in the SLAC electron beam-driven plasma wakefield acceleration (PWFA) experiments lead to very important understanding of the beam-plasma interaction. In particular, measurements as a function of the plasma length Lp show that the energy gain increases linearly with Lp in the 10 to 30 cm range. Based on this scaling, the plasma was subsequently lengthened to Lp=90cm, resulting in the first demonstration of the doubling of the energy of a fraction of the incoming 42GeV electrons*. The peak accelerating gradient is larger than 40GV/m and is sustained over meter-scale plasma lengths. These measurements also reveal that the optimum plasma density for acceleration is about 2.7·1017/cc, larger than the value predicted by the linear theory for the approximately 20 microns bunch length, confirming that the experiment is conducted in the non-linear regime of the PWFA. Detailed experimental results will be presented.
* "Energy doubling of 42 GeV electrons in a meter scale plasma wakefield accelerator", I. Blumenfeld et. al., Nature, 2006, accepted |
||
| THPMS034 | Generation and Characterization of the Microbunched Beams with a Wire Mesh Target | 3079 |
|
||
|
Funding: Work supported by US Department of Energy contract DE-AC02-98CH10886 The presentation will cover experimental results on generation and measurement of the beams with theμbunches length from 1 to 50 microns at Brookhaven Accelerator Test Facility. Arbitrary number of microbunches is sliced out of 5 ps long beam using wire mesh and slits. The details of beam structure are characterized using CSR interferometer and 6 mm long plasma wakefield channel with the controllable plasma density. |
||
| THPMS037 | ON THE POSSIBILITY OF ACCELERATING POSITRON ON AN ELECTRON WAKE AT SABER | 3082 |
|
||
|
Funding: This work was supported by the Department of Energy contract DE-FG02-92-ER40745 A new approach for positron acceleration in non-linear plasma wakefields driven by electron beams is presented. Positrons can be produced by colliding an electron beam with a thin foil target embedded in the plasma. Integration of positron production and acceleration in one stage is realized by a single relativistic, intense electron beam. Simulations with the parameters of the proposed SABER facility at SLAC suggest that this concept could be tested there. |
||
| THPMS038 | Magnetic Measurements and Simulations of a 4-Magnet Dipole Chicane for the International Linear Collider | 3085 |
|
||
| T-474 at SLAC is a prototype BPM-based energy spectrometer for the ILC. We describe magnetic measurements and simulations for the 4-magnet chicane used in T-474. The ILC physics program requires better than 100 part-per-million (ppm) accuracy for energy measurements, which necessitates better than 50 ppm accuracy for magnetic field integral measurements. A 4-dipole chicane is used in T-474 with mid-chicane dispersion of 5-mm and magnetic fields of ~1 kGauss; similar to the current ILC parameters. Stability, reproducibility and consistency of magnetic measurements, including magnetic field maps for the T-474 dipole magnets, are presented using a moving wire, rotating coil, NMR probe, Hall probe and low-field fluxgate magnetometer. Measurements from SLAC's Magnet Test Lab facility as well as in situ measurements in End Station A (ESA) are presented, including measurements of residual magnetic fields in the T-474 chicane between the chicane magnets. Results are provided for an operational mode with a 1-hour calibration cycle, where the chicane magnets are operated in both polarities and at near-zero field. | ||
| THPMS039 | Wakefield Effects in the Beam Delivery System of the ILC | 3088 |
|
||
|
Funding: Work supported by US Department of Energy contract DE-AC02-76SF00515 The main linac of the International Linear Collider (ILC) accelerates short, high peak current bunches into the Beam Deliver System (BDS) on the way to the interaction point. In the BDS wakefields are excited by the resistance of the beam pipe walls and by beam pipe transitions that will tend to degrade the emittance of the beam bunches. In this report we calculate the effect on emittance of incoming jitter or drift, and of misalignments of the beam pipes with respect to the beam axis, both analytically and through multi-particle tracking. Finally, we discuss ways of ameliorating the wake effects in the BDS. |
||
| THPMS040 | Correlation of Beam Parameters to Decelerating Gradient in the E-167 Plasma Wakefield Acceleration Experiment | 3091 |
|
||
|
Funding: This work was supported by the Department of Energy contracts DE-AC02-76SF00515, DE-FG02-92ER40727, DE-FG02-92-ER40745 DE-FG02-03ER54721, DE-FC02-01ER41179 and NSF grant Phy-0321345 Recent experiments at SLAC have shown that high gradient acceleration of electrons is achievable in meter scale plasmas. Results from these experiments show that the wakefield is sensitive to parameters in the electron beam which drives it. In the experiment the bunch length and beam waist location were varied systematically at constant charge. Here we investigate the correlation of peak beam current to the decelerating gradient. Limits on the transformer ratio will also be discussed. The results are compared to simulation. |
||
| THPMS041 | Disruption of Particle Detector Electronics by Beam Generated EMI | 3094 |
|
||
| The possibility that beam generated electromagnetic interference (EMI) could disrupt the operation of particle detector electronics has been of some concern since the inception of short pulse electron colliders more than 30 years ago, Some instances have been reported where this may have occurred but convincing evidence has not been available. This possibility is of concern for the ILC. We have conducted test beam studies demonstrating that electronics disruption does occur using the vertex detector electronics from the SLD detector which ran at the SLC at SLAC. We present the results of those tests and we describe the need for EMI standards, for beam and detector instrumentation, at the ILC. | ||
| THPMS047 | Emittance Growth from Multiple Coulomb Scattering in a Plasma Wakefield Accelerator | 3097 |
|
||
|
Funding: This work was supported by the Department of Energy contracts DE- AC02-76SF00515 Emittance growth is an important issue for plasma wakefield accelerators (PWFAs). Multiple Coulomb scattering (MCS) is one factor that contributes to this growth. Here, the MCS emittance growth of an electron beam traveling through a PWFA in the blow out regime is calculated. The calculation uses well established formulas for angular scatter in a neutral vapor and then extends the range of Coulomb interaction to include the effects of traveling through an ion column. Emittance growth is negligible for low Z materials; however, becomes important for high Z materials. |
||
| THPMS049 | Investigations of the Wideband Spectrum of Higher Order Modes Measured on TESLA-style Cavities at the FLASH Linac | 3100 |
|
||
|
Funding: US DOE Contract #DE-AC02-76SF00515 Higher Order Modes (HOMs) excited by the passage of the beam through an accelerating cavity depend on the properties of both the cavity and the beam. It is possible, therefore, to draw conclusions on the inner geometry of the cavities based on observations of the properties of the HOM spectrum. A data acquisition system based on two 20 GS/s, 6 GHz scopes has been set up at the FLASH facility, DESY, in order to measure a significant fraction of the HOM spectrum predicted to be generated by the TESLA cavities used for the acceleration of its beam. The HOMs from a particular cavity at FLASH were measured under a range of known beam conditions. The dipole modes have been identified in the data. 3D simulations of different manufacturing errors have been made, and it has been shown that these simulations can predict the measured modes. |
||
| THPMS050 | Designing Photonic Bandgap Fibers for Particle Acceleration | 3103 |
|
||
|
Funding: Supported by U. S. Dept. of Energy contract DE-AC02-76SF00515 Photonic bandgap (PBG) fibers with hollow core defects have been suggested for use as laser driven accelerator structures. The modes of a periodic PBG fiber lie in a set of allowed bands. A fiber with a central vacuum defect can support so-called defect modes with frequencies in the bandgap and electromagnetic fields confined spatially near the central defect. A defect mode suitable for relativistic particle acceleration must have a longitudinal electric field in the central defect and a phase velocity near the speed of light (SOL). We explore the design of the defect geometry to support well-confined accelerating modes in such PBG fibers. The details of the surface boundary separating the defect from the surrounding matrix are found to be the critical ingredients for optimizing the accelerating mode properties. We give examples of improved accelerating modes in fiber geometries with modified defect surfaces. |
||
| THPMS052 | Optical Wakefield from a Photonic Bandgap Fiber Accelerator | 3106 |
|
||
| Photonic Bandgap (PBG) structures have recently been proposed as optical accelerators for there high coupling impedance and high damage threshold (>2 GV/m). As a first step in preparing a PBG accelerator, we propose to first observe the optical wakefield induced incoherently by an electron beam traversing the structure in the absence of a coupled laser pulse. The electrons are coupled into the fiber via a permanent magnet quadrupole triplet. The electrons excite fiber modes with speed-of-light phase velocities. By observing the wakefield using a spectrometer, the accelerating mode frequencies are determined. | ||
| THPMS053 | Compensation of the Effect of a Detector Solenoid on the Beam Size in the ILC | 3109 |
|
In the International Linear Collider (ILC) [1] the colliding beams must be focused to the nanometre size in order to reach the desired luminosity. The method of Weak Antisolenoid is used for the compensation of the effect of the Detector Solenoid on the beam size [2, 3]. The studies of this method require the computer simulation of the charged particle's kinematics in the arbitrarily distributed solenoidal, dipole, quadrupole and higher multipole fields. We suggest the mathematical algorithm that allows to optimize parameters of antisolenoid for different configurations of Final Focus magnets and to compensate parasitic effects of the Detector Solenoid on the beam.
[1] 'International Linear Collider Reference Design Report', April 2007 |
||
| THPMS054 | Study of Lattice Beams and their Limitations | 3112 |
|
||
|
Funding: Work supported by U. S. Dept. of Energy contract DE-AC02-76SF00515. Luminosity considerations for microscale accelerators intended for high-energy physics place a high premium on the bunch repetition rate and phase space density at the interaction point. The NLC Test Accelerator (NLCTA) at SLAC was built to address such beam dynamics issues for the Next Linear Collider and beyond. Because an S-Band RF gun has been installed together with a low-energy, high-resolving power spectrometer (LES), it is useful to explore alternatives to conventional scenarios with it. We consider possibilities that can be tested with minimal modification to this system e.g. cases that involve producing multiple bunches from the cathode in different formats such as a 2D planar matrix or 3D tensor beam made of smaller bunches or bunchlets that replace the usual, single higher charge bunches. Thus, we study configurations of interacting bunchlets nij or nijk coming from the cathode and passing through the emittance compensating solenoids that can be matched to the linac or focussed on the LES focal plane at 6 MeV. Parmela calculations have been done that show no significant space charge effects or emittance increases for pC bunchlet charges. |
||
| THPMS055 | Beam Dynamics Measurements for the SLAC Laser Acceleration Experiment | 3115 |
|
||
|
Funding: Work supported by U. S. Dept. of Energy contract DE-AC02-76SF00515. The NLC Test Accelerator (NLCTA) at SLAC was built to address various beam dynamics issues for the Next Linear Collider. An S-Band RF gun has been installed with diagnostics and a low energy spectrometer (LES) at 6 MeV together with a large-angle extraction line at 60 MeV. This is followed by a matching section, buncher and final focus for the laser acceleration experiment, E163. The laser-electron interaction area is followed by a broad range (2\%), high resolving power (104) spectrometer (HES) for electron bunch analysis. Emittance compensating solenoids and the LES are used to tune for best operating point and match to the linac. Optical symmetries in the design of the 25.5° extraction line provide 1:1 phase space transfer without use of sextupoles for a large, 6D phase space volume and range of input conditions. Spot sizes of a few microns at the IP (or HES object) allow tests of microscale structures as well as high resolving power at the image of the HES. Tolerances, tuning sensitivities and diagnostics are discussed together with the latest commissioning results and their comparison to design expectations. |
||
| THPMS056 | Emittance Preservation in the International Linear Collider Ring to Main Linac Transfer Line | 3118 |
|
||
|
Funding: Work supported by the US Department of Energy, contract DE-AC02-76SF00515. The very small vertical beam emittance in the International Linear Collider (ILC) can be degraded by dispersion, xy coupling, transverse wakefields, and time-varying transverse fields introduced by elements with misalignments, strength errors, xy rotation errors, or yz rotation errors in the Ring to Main Linac (RTML) transfer line. We present a plan for emittance preservation in this beamline which uses local, quasi-local, and global correction schemes. Results of simulations of the emittance preservation algorithm are also presented and discussed. |
||
| THPMS059 | Correlating Pulses from Two Spitfire, 800nm Lasers | 3121 |
|
||
|
Funding: Department of Energy contracts DE-AC02-76SF00515, DE-FG03-97ER41043-III
The E163 laser acceleration experiments conducted at SLAC have stringent requirements on the temporal properties of two regeneratively amplified, 800nm, Spitfire laser systems. To determine the magnitude and cause of timing instabilities between the two Ti:Sapphire amplifiers, we pass the two beams through a cross-correlator and focus the combined beam onto a Hamamatsu G1117 photodiode. The photodiode has a bandgap such that single photon processes are suppressed and only the second order, two-photon process produces an observable response. The response is proportional to the square of the intensity. The diode is also useful as a diagnostic to determine the optimal configuration of the compression cavity.
Yoshihiro Takagi et al, 'Multiple- and Single-shot autocorrelator based on two-photon conductivity in semiconductors.' Optics Letters, Vol. 17, No. 9, May 1, 1992. |
||
| THPMS060 | Transport Optics Design and Multi-particle Tracking for the ILC Positron Source | 3124 |
|
||
|
Funding: U. S. DOE Contract DE-AC02-76SF00515 Undulator-based positron source is adopted as the International Linear Collider baseline design. Complete optics to transport the positron beam having large angular divergence and large energy spread from a thin Ti target to the entrance of the 5 GeV damping ring injection line is developed. Start-to-end multi-particle tracking through the beamline is performed including the optical matching device, capture accelerator system, transport system, superconducting booster linac, spin rotators, and energy compressor. Positron capture efficiency of different schemes (immersed vs shielded target, and flux concentrator vs quarter wave transformation for the optics matching system) is compared. For the scheme of a shielded target and quarter wave transformation, the simulation shows that 15.1% of the positrons from the target are captured within the damping ring 6-D acceptance at the entrance of the damping ring injection line. |
||
| THPMS061 | Design of a High-current Injector and Transport Optics for the ILC Electron Source | 3127 |
|
||
|
Funding: U. S. DOE Contract DE-AC02-76SF00515 A train of 2-nsμbunches are generated in the DC-gun based injector in the ILC e- source; a bunching system with extremely high bunching efficiency to compress bunch down to 20 ps FWHM is designed. Complete optics to transport the electron beam to the 5-GeV damping ring injection line is developed. Start-to-end multi-particle tracking through the beamline is performed including the bunching system, pre-acceleration, chicane, 5-GeV SC booster linac, spin rotators and energy compressor. It shows more than 95% of electrons from the DC-gun are captured within the 6-D damping ring acceptance at the entrance of damping ring injection line. The field and alignment errors, and orbit correction are analyzed. |
||
| THPMS064 | Lifetime Measurements of High Polarization Strained-Superlattice Gallium Arsenide at Beam Current > 1 Milliamp using a New 100kV Load Lock Photogun | 3130 |
|
||
|
Funding: Authored by Jefferson Science Associates, LLC under U. S. DOE Contract No. DE-AC05-06OR23177.
A new 100 kV GaAs DC Load Lock Photogun has been constructed at Jefferson Laboratory, with improvements for photocathode preparation and for operation in a high voltage, ultra-high vacuum environment. Although difficult to gauge directly, we believe that the new gun design has better vacuum conditions compared to the previous gun design, as evidenced by longer photocathode lifetime, that is, the amount of charge extracted before the quantum efficiency of the photocathode drops by 1/e of the initial value via the ion back-bombardment mechanism. Photocathode lifetime measurements at DC beam intensity of up to 10 mA have been performed to benchmark operation of the new gun and for fundamental studies of the use of GaAs photocathodes at high average current*. These measurements demonstrate photocathode lifetime longer than one million Coulombs per square centimeter at a beam intensity higher than 1 mA. The photogun has been reconfigured with a high polarization strained superlattice photocathode (GaAs/GaAsP) and a mode-locked Ti:Sapphire laser operating near band-gap. Photocathode lifetime measurements at beam intensity greater than 1 mA are measured and presented for comparison.
"Further Measurements of Photocathode Operational Lifetime at Beam Intensity >1mA using the CEBAF 100 kV DC GaAs Photogun", J. Grames et al., Proc. of the 17th Inter. Spin Symposium, Japan (2006). |
||
| THPMS067 | A CW Positron Source for CEBAF | 3133 |
|
||
|
Funding: Authored by Jefferson Science Associates, LLC under U. S. DOE Contract No. DE-AC05-06OR23177. A positron source for the 6 GeV (or the proposed 12 GeV upgrade) recirculating linacs at Jefferson Lab is presented. The proposed 100nA CW positron source has several unique characteristics; high incident beam power (100kW), 10 MeV incident electron beam energy, CW incident beam and CW production. Positron production with 10 MeV electrons has several advantages; the energy is below neutron threshold so the production target will not become activated during use and the absolute energy spread is bounded by the low incident energy. These advantages are offset by the large angular distribution of the outgoing positrons. Results of simulations of the positron production, capture, acceleration and injection into the recirculating linac are presented. Energy flow and thermal management of the production target present a challenge and are included in the simulations. |
||
| THPMS068 | Systems Testing of a Free Hg Jet System for Use in a High-Power Target Experiment | 3136 |
|
||
|
Funding: U. S. Deparment of Energy contract DE-AC05-00OR22725 The design and operational testing of a mercury jet delivery system is presented. The equipment is part of the Mercury Intense Target (MERIT) Experiment, which is a proof-of-principle experiment to be conducted at CERN in the summer of 2007 to determine the feasibility of using an unconstrained jet of mercury as a target in a Neutrino Factory or Muon Collider. The Hg system is capable of producing a 1 cm diameter, 20 m/s jet of Hg inside a high-field solenoid magnet. A high-speed optical diagnostic system allows observation of the interaction of the jet with a 24 GeV proton beam. Performance of the Hg system will be presented, along with results of integrated systems testing without a beam. |
||
| THPMS069 | The New ORNL Multicharged Ion Research Facility Floating Beamline | 3139 |
|
||
|
Funding: Sponsored by the OBES and the OFES of the U. S. DOE under contract No. DE-AC05-00OR22725 with UT-Battelle, LLC. MRF was appointed through the ORNL Postdoctoral Research Associates Program administered jointly by ORISE and ORNL.
We report on the development and implementation of a new beam line floatable at up to -15 kV and injected by a 10 GHz CAPRICE ECR ion source at the ORNL Multicharged Ion Research Facility MIRF as part of a major facility upgrade project [1]. With the floating beamline operating at negative high voltage, and the ECR source at ground potential, intense dc beam deceleration into grounded experimental chambers to energies as low as a few eV/q is made possible. The primary application of these ion beams is to study fundamental collisional interactions [2] of multicharged ions with electrons, atoms, and surfaces. Design details of the floating beam line, including source extraction, deceleration optics and voltage isolation will be presented at the conference. The novel features of a LABVIEW-based supervisory control and data acquisition (SCADA) system developed for the floating beam line will be described as well.
[1]F. W. Meyer et al. "The ORNL MIRF Upgrade project," NIMB B242,71(2006).[2]F. W. Meyer,"ECR-Based Atomic Collisions Research at ORNL MIRF," in Trapping Highly Charged Ions: Fundamentals & Applications, Nova Sci. Pub., New York, 2000, pp. 117-164. |
||
| THPMS070 | High Power Testing of a Fully Axisymmetric RF Gun | 3142 |
|
Funding: This work was funded under an SBIR contract from the US Department of Energy. High power RF testing has been performed on a novel axisymmetric radiofrequency electron gun at a frequency of 11.43 GHz using the magnicon facility at the Naval Research Laboratory. This gun utilizes coaxial coupling from the upstream end of unit and allows for axisymmetric tuning of both the cathode cell and the second cell. The features of the gun have been proven to operate at high gradients. The overall design of the gun will be discussed along with the results of the high power RF testing. |
||
| THPMS071 | Laser-Powered Dielectric Structure as a Micron-Scale Electron Source | 3145 |
|
||
|
We describe a resonant laser-powered structure, measuring 1 mm or less in every dimension, that is capable of generating and accelerating electron beams to low energies (~1-2 MeV). Like several other recently investigated dielectric-based accelerators,* the device is planar and resonantly excited with a side-coupled laser; however, extensive modifications are necessary for synchronous acceleration and focusing of nonrelativistic particles. Electrons are generated within the device via a novel ferroelectric-based cathode. The accelerator is constructed from dielectric material using conventional microfabrication techniques and powered by a 1μm gigawatt-class laser. The electron beams produced are suitable for a number of existing industrial and medical applications.
*R. Yoder and J. Rosenzweig, Phys. Rev. STAB 8, 111301 (2005); Z. Zhang et al., Phys. Rev. STAB 8, 071302 (2005); A. Mizrahi and L. Schachter, Phys. Rev. E 70, 016505 (2004). |
||
| THPMS072 | Superconducting Traveling Wave Ring with High Gradient Accelerating Section | 3148 |
|
||
| Considerable gain of a superconducting linac accelerating gradient provides using of a traveling wave structure instead of a standing wave accelerating section. Preservation of the superconducting structure advantages requires to put the TW accelerating section into a superconducting traveling wave ring (STWR). We discuss two variants of the STWR with one and two feeding couplers. The STWR application allows to increase the superconducting section accelerating gradient up to ~50 MV/m and essentially reduce the price of the section tuning system. | ||
| THPMS073 | Progress towards a Gap Free Dielectric-Loaded Accelerator | 3151 |
|
||
|
One of the major concerns in the development of Dielectric-Loaded Accelerating (DLA) structures is the destructive breakdown at dielectric joints caused by a local electric field enhancement induced by the discontinuity of the dielectric constant on the surface of the joint gap. Our previous X-band traveling wave DLA structure design*, for example, incorporated two separate impedance matching sections with at least two dielectric joints. In this paper, we present a new design to avoid this problem. This scheme is based on a coaxial type coupler which is able to implement mode conversion and impedance matching at the same time and therefore to eliminate joint gap induced breakdown. The new structure is under construction; bench test results will be presented
* C. Jing, W. Gai, J. Power, R. Konecny, S. Gold, W. Liu and A. Kinkead, IEEE, Trans. PS, vol.33 No.4, Aug. 2005, pp.1155-1160. |
||
| THPMS074 | High Transformer Ratios in Collinear Wakefield Accelerators | 3154 |
|
||
|
Funding: DOE SBIR Phase II, DE-FG02-02ER83418. Based on our previous experiment that successfully demonstrated wakefield transformer ratio enhancement in a 13.625 GHz dielectric-loaded collinear wakefield accelerator using the ramped bunch train technique, we present here a redesigned experimental scheme for even higher enhancement of the efficiency of this accelerator. Design of a collinear wakefield device with a transformer ratio R>>2, is presented. Using a ramped bunch train (RBT) rather than a single drive bunch, the enhanced transformer ratio (ETR) technique is able to increase the transformer ratio R above the ordinary limit of 2. To match the wavelength of the fundamental mode of the wakefield with the bunch length (σz=2 mm) of the new Argonne Wakefield Accelerator (AWA) drive gun, where the experiment will be performed, a 26.625 GHz dielectric based accelerating structure is required. This transformer ratio enhancement technique based on our dielectric-loaded waveguide design will result in a compact, high efficiency accelerating structure for future wakefield accelerators. |
||
| THPMS075 | High Power Testing of a Fused Quartz-based Dielectric-loaded Accelerating Structure | 3157 |
|
||
| We report on the most recent results from a series of high power tests being carried out on RF-driven dielectric-loaded accelerating (DLA) structures. The purpose of these tests is to determine the viability of the DLA as a traveling-wave accelerator and is a collaborative effort between Argonne National Laboratory (ANL), Naval Research Laboratory (NRL), and Stanford Linear Accelerator Center (SLAC). In this paper, we report on the recent high power tests of a fused quartz-based DLA structure that was carried out at incident powers of up to 12 MW at NRL and 37 MW at SLAC. We report experimental details of the RF conditioning process and make comparison of our multipactor model to the experiment, including tests of geometrical scaling laws and the time evolution of multipactor. Finally, we discuss future plans for the program including a planned test of new quartz-based DLA with a different geometry to both reach higher accelerating gradients and to continue the parametric study of multipactor. | ||
| THPMS076 | Development of Dual Layered Dielectric-Loaded Accelerating Structure | 3160 |
|
||
|
Funding: DOE SBIR Phase I, DOE Grant No. DE-FG02-05ER84356
Due to the high magnetic field-induced surface currents on its conducting sleeve, a conventional single layer Dielectric-Loaded Accelerating (DLA) structure exhibits a relatively high RF loss. One possible way to solve this problem is to use multilayered DLA structures*. In these devices, the RF power attenuation is reduced by making use of the Bragg Fiber concept: the EM fields are well confined by multiple reflections from multiple dielectric layers. This paper presents the design of an X-band dual layer DLA structure as well as the results of bench tests of the device. We will also present results on the design, numerical modeling, and fabrication of structures for coupling RF into multilayer DLAs such as a novel TM03 mode launcher and a TM01-TM03 mode converter using dielectric-loaded corrugated waveguide.
* C. Jing, W. Liu, W. Gai, J. G. Power, and T. Wong, Nucl. Instr. Meth. Phy. Res. A 539 (2005) 445-454. |
||
| THPMS077 | Progress towards Development of a Diamond-Based Cylindrical Dielectric Accelerating Structure | 3163 |
|
||
|
Funding: This research is supported by the US Department of Energy In this talk, we present our recent developments on a high gradient diamond-based cylindrical dielectric loaded accelerator (DLA). The final goal of this research is to achieve a record accelerating gradient (~ 600 MV/m) in a demonstration of the structure at high power and with accelerated beam. We discuss here a new technology for the development of cylindrical diamond-based waveguides and the design, fabrication and high power testing of a cylindrical diamond-based DLA accelerating structure. The electrical and mechanical properties of diamond make it an ideal candidate material for use in dielectric accelerators: high RF breakdown level, extremely low dielectric losses and the highest thermoconductive coefficient available. Multipacting of the CVD diamond can be suppressed by diamond surface dehydrogenation. A plasma supported Chemical Vapor Deposition (CVD) technology to produce low loss high quality cylindrical diamond layers is presented. Special attention is devoted to the numerical optimization of the coupling section, where the surface magnetic and electric fields are minimized relative to the accelerating gradient and within known metal surface breakdown limits. |
||
| THPMS078 | Status of the Microwave PASER Experiment | 3166 |
|
||
|
Funding: Work supported by US Department of Energy The PASER is a new method for particle acceleration, in which energy from an active medium is transferred to a charged particle beam. The effect is similar to the action of a maser or laser with the stimulated emission of radiation being produced by the virtual photons in the electromagnetic field of the beam. We are developing a demonstration PASER device operating at X-band, based on the availability of a new class of active materials that exhibit photoinduced electron spin polarization. We will report on the status of active material development and measurements, numerical simulations, and preparations for microwave PASER experiments at the Argonne Wakefield Accelerator facility. |
||
| THPMS079 | Nonlinear Permittivity Effects in Dielectric Accelerating Structures | 3169 |
|
||
|
Funding: Work supported by the US Department of Energy
New low loss ferroelectric ceramic materials* possessing large variations in the permittivity as a function of the electric field present interesting and potentially useful applications for dielectric loaded accelerating structures, both wakefield-based and driven by an external rf source. We will consider X-band cylindrical dielectric structures and report numerical results on frequency multiplication, wave steepening and shock formation, and the effect of nonlinearities on the mode structure of these devices. We will examine applications of nonlinear dielectric devices to high gradient acceleration, rf sources, and beam diagnostics.
* ''Fast Switching Ferroelectric Materials for Accelerator Applications'', A. Kanareykin et al., Proceedings of Advanced Accelerator Concepts 2006 (in press) |
||
| THPMS080 | Inverse-Transition Radiation Laser Acceleration Experiments at SLAC | 3172 |
|
||
| We present a series of laser-driven particle acceleration experiments that are aimed at studying laser-particle acceleration as an inverse-radiation process. To this end we employ a semi-open vacuum setup with a thin planar boundary that interacts with the laser and the electromagnetic field of the electron beam. Particle acceleration from different types of boundaries will be studied and compared to the theoretical expectations from the Inverse-radiation picture and the field path integral method. We plan to measure the particle acceleration effect from transparent, reflective, black, and rough surface boundaries. While the agreement between the two acceleration pictures is straightforward to prove analytically for the transparent and reflective boundaries the equivalence is not clear-cut for the absorbing and rough-surface boundaries. Therefore, experimental observation may be the most reliable method for establishing the appropriate model for the interaction of the laser field with the particle beam in the presence of a loaded vacuum structure. | ||
| THPMS081 | Proposed Few-cycle Laser-particle Accelerator Structure | 3175 |
|
||
| We describe a proposed transparent dielectric grating accelerator structure that is designed for ultra-short laser pulse operation. The structure is not a waveguide, but rather it is based on the principle of periodic field reversal to achieve phase synchronicity for relativistic particles. To preserve ultra-short pulse operation it does not resonate the laser field in the vacuum channel. The geometry of the structure appears well suited for application with high average power lasers and high thermal loading. It shows potential for an unloaded gradient of several GeV/m with 10 fsec laser pulses and the possibility to accelerate high bunch charges. The fabrication procedure and proposed near-term experiments with this accelerator structure are presented. | ||
| THPMS082 | Muon Acceleration to 750 GeV in the Tevatron Tunnel for a 1.5 TeV mu+ mu- Collider | 3178 |
|
||
|
Funding: Work supported by DE-FG02-91ER40622 and DE-AC02-98CH10886. Muon acceleration from 30 to 750 GeV in 72 orbits using two rings in the 1000m radius Tevatron tunnel is explored. The first ring ramps at 400 Hz and accelerates muons from 30 to 400 GeV in 28 orbits using 14 GV of 1.3 GHz superconducting RF. The ring duplicates the Fermilab 400 GeV main ring FODO lattice, which had a 61m cell length. Muon survival is 80%. The second ring accelerates muons from 400 to 750 GeV in 44 orbits using 8 GV of 1.3 GHz superconducting RF. The 30 T/m main ring quadrupoles are lengthened 87% to 3.3m. The four main ring dipoles in each half cell are replaced by three dipoles which ramp at 550 Hz from -1.8T to +1.8T interleaved with two 8T fixed superconducting dipoles. The ramping and superconducting dipoles oppose each other at 400 GeV and act in unison at 750 GeV. Muon survival is 92%. Two mm copper wire, 0.28mm grain oriented silicon steel laminations, and a low duty cycle mitigate eddy current losses. Low emittance muon bunches allow small aperatures and permit magnets to ramp with a few thousand volts. Little civil construction is required. The tunnel exists. |
||
| THPMS083 | The EMMA Lattice Design | 3181 |
|
||
|
Funding: Work Supported by the United States Department of Energy, Contract No. DE-AC02-98CH10886. EMMA is a 10 to 20 MeV electron ring designed to test our understanding of beam dynamics in a relativistic linear non-scaling fixed field alternating gradient accelerator (FFAG). This paper describes the design of the EMMA lattice. We begin with a description of the experimental goals that impact the lattice design. We then describe what motivated the choice for the basic lattice parameters, such as the type of cells, the number of cells, and the RF frequency. We next list the different configurations that we wish to operate the machine in so as to accomplish our experimental goals. Finally, we enumerate the detailed lattice parameters, showing how these parameters result from the various lattice configurations. |
||
| THPMS086 | Plasma Lens for US Based Super Neutrino Beam at Either FNAL or BNL | 3184 |
|
||
|
Funding: Work supported under Contract No. DE-AC02-98CH1-886 with the US Department of Energy Plasma lens concept is examined as an alternative to focusing horns and solenoids for a neutrino beam facility. The concept is based on a combined high-current lens/target configuration. Current is fed at an electrode located downstream from the beginning of the target where pion capturing is needed. Some of the current flows through the target, while the rest is carried by plasma outside the target. A second plasma lens section, with an additional current feed, follows the target. Plasma of this section is immersed in a solenoidal magnetic field to facilitate its current profile shaping to optimize pion capture. Simulation of the second section alone yielded a 10% higher neutrino production than the horn system. Plasma lenses have additional advantages: larger axial currents, high signal purity: minimal neutrino background in anti-neutrino runs. Lens medium consists of plasma, consequently, particle absorption and scattering is negligible. Withstanding high mechanical and thermal stresses is not an issue. Results of capturing and focusing obtained for various plasma lens configurations will be presented. |
||
| THPMS087 | Low Emittance Electron Beams for the RHIC Electron Cooler | 3187 |
|
||
|
Funding: Work performed under the United Staes Department of Energy Contract No. DE-AC02-98CH1-886. An electron cooler, based on an Energy Recovery Linac (ERL) is under development for the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. This will be the first electron cooler operating at high energy with bunched beams. In order to achieve sufficient cooling of the ion beams the electron have to have a charge of 5 nC and a normalized emittance less than 4 mm mrad. This paper presents the progress in optimizing the injector and the emittance improvements from shaping the charge distribution in the bunch. |
||
| THPMS088 | Emittance Compensation for Magnetized Beams | 3190 |
|
||
|
Funding: Work performed under the United Staes Department of Energy Contract No. DE-AC02-98CH1-886.
Emittance compensation is a well established technique* for minimizing the emittance of electron beam from a RF photo-cathode gun. Longitudinal slices of a bunch have a small emittance, but due to the longitudinal charge distribution of the bunch and time dependent RF fields they are not focused in the same way, so that the direction of their phase ellipses diverges in phase space and the projected emittance is much larger. Emittance compensation reverses the divergence. At the location where the slopes of the phase ellipses coincides the beam is accelerated, so that the space charge forces are reduced. A recipe for emittance compensation is given in reference**. For magnetized beams (where the angular momentum is non-zero) such emittance compensation is not sufficient because variations in the slice radius lead to variations in the angular speed and therefore to an increase of emittance in the rotating frame. We describe a method and tools for a compensation that includes the beam magnetization.
* L. Serafini, J. B. Rosenzweig, Phys. Rev E 55, 7565, (1997) |
||
| THPMS090 | A Complete Scheme of Ionization Cooling for a Muon Collider | 3193 |
|
||
|
Funding: Work Supported by the United States Department of Energy, Contract No. DE-AC02-98CH10886. We propose a complete scheme for cooling a muon beam for a muon collider. We first outline the parameters required for a multi-TeV muon collider. The cooling scheme starts with the front end of the Study 2a proposed Neutrino Factory. This yields bunch trains of both muon signs. Emittance exchange cooling in upward climbing helical lattices then reduces the longitudinal emittance until it becomes possible to combine the trains into single bunches, one of each sign. Further cooling is now possible in emittance exchange cooling rings. Final cooling to the required parameters is achieved in 50 T solenoids that use high temperature superconductor. Preliminary simulations of each element will be presented. |
||
| THPMS091 | The Superconducting Magnets of the ILC Beam Delivery System | 3196 |
|
||
|
Funding: Work supported by the US Department of Energy under contract DE-AC02-98CH10886. A wide variety of superconducting magnets are needed in the ILC Beam Delivery System (BDS) to maximize luminosity and minimize experimental backgrounds. Compact final focus quadrupoles and multifunction correction coils are used with 14 mr total crossing angle to focus incoming beams to few nanometer spot sizes while focusing outgoing disrupted beams into a separate extraction beam line. Large aperture anti-solenoids correct deleterious nonlinear effects that arise due to the overlap of focusing fields with the main detector solenoid. Far from the interaction point (IP) sets of strong small aperture octupoles help minimize backgrounds at the IP due to beam halo particles while weak large aperture dipoles integrated with the experimental detector reduce backgrounds due to beamstrahlung pairs generated at the IP. The physics requirements and magnetic design solutions for these magnets are reviewed in this paper. |
||
| THPMS092 | Superconducting Non-Scaling FFAG Gantry for Carbon/Proton Cancer Therapy | 3199 |
|
||
|
Funding: * Supported by the U. S. Department of Energy under Contract No. DE-AC02-98CH10886. ** Work supported by the U. S. Department of Energy under Contract No. DE-AC02-05CH11231 We report on improvements in the non-scaling Fixed Field Alternating Gradient (FFAG) gantry design. As we previously reported*, a major challenge of the carbon/proton cancer therapy facilities is isocentric gantry design. The weight of the isocentric gantry transport elements in the latest Heidelberg carbon/proton facility is 135 tons**. In this report we detail improvements to the previous non-scaling gantry design. We estimate that this non-scaling FFAG gantry would be almost hundred times lighter than traditional heavy ion gantries. Very strong focusing with small dispersion permits passage of different energies of carbon beams through the gantry's fixed magnetic field.* |
||
| THPMS093 | Muon Acceleration with the Racetrack FFAG | 3202 |
|
Funding: Supported by the U. S. Department of Energy under Contract No. DE-AC02-98CH10886. Muon acceleration for muon collider or neutrino factory is still in the stage where further improvements are likely as a result of further study. This report presents a design of the racetrack non-scaling Fixed Field Alternating Gradient (NS-FFAG) accelerator to allow fast muon acceleration in small number of turns. The racetrack design is made of four arcs: two arcs at opposite sides have a smaller radius and are made of closely packed combined function magnets, while two additional arcs with a very large radius are used for muon extraction, injection, and RF accelerating cavities. The ends of the large radii arcs are geometrically matched at the connections to the arcs with smaller radii. The dispersion and both horizontal and vertical amplitude functions are matched at the central energy. |
||
| THPMS094 | Acceleration of Electrons with the Racetrack Non-Scaling FFAG for e-RHIC | 3205 |
|
||
|
Funding: Supported by the U. S. Department of Energy under Contract No. DE-AC02-98CH10886 Acceleration of electrons up to 10 GeV for a future electron-ion collider eRHIC (Relativistic Heavy Ion Collider) could be performed with the energy recovery linac with multiple passes. An energy recovery scheme is required if a superconducting linac is used for acceleration. We report on an attempt to make a combination of a multi-pass linac with non-scaling Fixed Field Alternating Gradient (NS-FFAG) arcs. Two NS-FFAG arcs would allow electrons to pass through the same structure with different energies. The beam will be accelerated by the superconducting linac at the top of the sine function, and returned to the front of the linac by the non-scaling FFAG. This process is repeated until the total energy of 10 GeV is reached. After collisions the beam is brought back by the NS-FFAG and decelerated before being dumped. |
||
| THPMS095 | Experimental Demonstration of Feasibility of a Polarized Gamma-source for ILC Based on Compton Backscattering Inside a CO2 Laser Cavity | 3208 |
|
||
|
Funding: Work supported by US Department of Energy contract DE-AC02-98CH10886
Compton interaction point incorporated into a high-average-power laser cavity is the key element of the Polarized Positron Source (PPS) concept proposed for ILC [1]. According to this proposal, circularly polarized gamma rays are produced in Compton backscattering from a 6 GeV linac e-beam inside a CO2 laser amplifier cavity. Intra-cavity positioning of the interaction point allows multiple laser recycling to match the electron bunch train format. We conducted experimental tests of multi-pulse operation of such active Compton cavity upon injection of a picosecond CO2 laser beam. Together with earlier demonstration of a high x-ray yield via the e-beam/CO2-laser backscattering, these new results show a viability of the entire PPS concept and closely prototype the laser source requirements for ILC.
[1] V. Yakimenko and I. V. Pogorelsky, Phys. Rev. ST Accel. Beams 9, 091001 (2006) |
||
| THPMS096 | Development of a Dielectric-Loaded Test Accelerator | 3211 |
|
||
|
Funding: Work supported by DoE and ONR.
A joint project is underway by the Naval Research Laboratory (NRL) and Argonne National Laboratory (ANL), in collaboration with the Stanford Linear Accelerator Center (SLAC), to develop a compact X-band accelerator for testing dielectric-loaded accelerator (DLA) structures.* The accelerator will use a 5-MeV injector previously developed by the Tsinghua University in Beijing, China, and will accommodate test structures up to 0.5 m in length. Both the injector and the structures will be powered by an 11.4-GHz magnicon amplifier that can produce 25 MW, 200-ns output pulses at up to 10 Hz. The injector will require ~5 MW of rf power, leaving ~20 MW to power the test structures. This paper will present a progress report on the construction and commissioning of the test accelerator, which will be located in a concrete bunker in the Magnicon Facility at NRL.
* S. H. Gold et al., Proc. PAC 2005. |
||
| THPMS097 | Laser Plasma Acceleration Experiment at the Naval Research Laboratory | 3214 |
|
||
| The traditional long term strategy for producing high quality electron beams in a single stage LWFA involves three elements: operation in the resonant or standard regime, the use of optical guiding to extend the acceleration region, and external injection of a precisely-phased, high quality injection electron bunch. The standard regime and optical guiding has been studied by many research groups and promise good results for the acceleration. The creation of the electron beam for external injection is still a very problematic issue. Recently, quasi-monoenergetic acceleration of particles from the background plasma has been observed in simulations and experiments operating in a shorter pulse regime. Such quasi-monoenergetic electrons could be a candidate for injection into a following stage of standard LWFA. We are in the initial stage of experiments to generate injection electrons using the HD-LIPA schemes with a 10 TW 50 fs laser system. The second stage accelerator is a capillary discharge plasma channel for extended acceleration distance. Preliminary results, including statistics on the stability of quasi-monoenergetic acceleration, will be presented. |